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1.
Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ 13C values (?12.5 to?6.8 ‰ Vienna Pee Dee Belemnite (VPDB)) record the predominant C 3 vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ 18O values (?7.8 to?3.4‰ VPDB) of all the NFC. Similar seasonal variations of δ 18O values for monthly NFC samples from the Swiss sites and those of mean monthly δ 18O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions. 相似文献
2.
Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments – Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave) – were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ 13C (average?28.2‰) and δ 18O (average?18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO 2 in a highly alkaline solution and consequent disequilibrium precipitation of CaCO 3. The main source of carbon is atmospheric or biogenic CO 2 in the poorly ventilated karstic cave, which is reflected in even lower δ 13C values. Statistical analysis of δ 13C and δ 18O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate. 相似文献
3.
Stable isotopes of water ( δ2H, δ18O) and δ13C TIC were used as a tool to trace the recharge processes, natural carbon (organic and inorganic) source and dynamics in the aquifers of the central Gangetic basin, India. Stable isotope ( δ2H, δ18O) record of groundwater ( n?=?105) revealed that the groundwater of Piedmont was recharged by meteoric origin before evaporation, while aquifers of the older and younger alluvium were recharged by water that had undergone evaporation loss. River Ganges and its tributaries passing through this area have very little contribution in recharging while ponds play no role in the recharging of adjacent aquifers. The connectivity of shallow aquifers of aquitard formation (comprised of clay/sandy clay with thin patches of fine grey sand), i.e. 25–60?m below ground level (bgl) with the main upper aquifer (at a depth of >120?m?bgl) was found to be higher in older and younger alluvium. Negative values of δ13C TIC (median ?9.6 ‰; range ?13.2 to ?5.4 ‰) and high TIC (median 35?mM; range 31–46?mM) coupled with low TOC (median 1.35?mg/L; range 0.99–1.77?mg/L) indicated acceleration in microbial activity in the younger alluvium, especially in the active floodplain of river Ganges and its proximity. 相似文献
4.
The routine methods for stable oxygen and hydrogen isotope analysis of water involve water–CO 2 gas equilibration and water reduction on hot metal (e.g. Zn, Cr, U) and subsequent mass spectrometric analysis of the evolved gases of CO 2 and H 2 for 18O/ 16O and 2H/ 1H ratios, respectively. Precise determination of the isotopic composition of water in brines with application of these standard methods is still problematic and technically often impossible due to detrimental influence of dissolved salts. The new method of brine desalination presented in this study overcomes the problem of the isotope salt effects encountered during the application of the routine techniques for the determination of the isotopic composition of high saline waters. The procedure combines two technical steps: (i) the chemical precipitation of Mg and Ca ions as insoluble non-hydroscopic fluorides, and (ii) the vacuum distillation of water from solution–precipitate mixture. The application of simple vacuum distillation allows full extraction of water and dehydration of remaining salts in a temperature range from 300 to 350?°C without hydrogen and oxygen isotope fractionation. The precision and accuracy of δ 18O and δ 2H determination of saline waters and brines with prior application of AgF desalination procedure is comparable with that usually obtained for fresh waters. 相似文献
5.
ABSTRACTWe investigated the influence of post-collection changes and snow gauge undercatch on the stable isotopic compositions of winter precipitation. Post-collection changes by evaporation or sublimation can be severe, and may be minimized, but not eliminated, by emptying collection gauges immediately after snowfall. Snow gauge undercatch caused two main effects: a small direct effect caused by preferential separation of snow particles during snowfall, and a much larger effect on the measured stable isotopic compositions of average annual precipitation as a result of under representation of winter precipitation. Despite these effects, however, we found little change to calculated local meteoric water lines (LMWL) for Saskatoon, SK, Canada. A comprehensive 27-year LMWL for Saskatoon which incorporates these effects can be described by δ2H?=?7.69?±?0.096?×? δ18O?–?2.22?±?1.72 ( r2?=?0.97, n?=?208). 相似文献
7.
ABSTRACTWe studied natural and forestry-drained peatlands to examine the effect of over 34 years lowered water table on the δ13C values of vegetation, bulk peat and subsoil. In the seven studied sites, δ13C in the basal peat layer was 1.1 and 1.2?‰ lower than that of the middle-layer and surface layer, respectively. Furthermore, there was a positive correlation between the δ13C values of the basal and surface peat layers, possibly due to carbon (C) recycling within the peat column. In the same mire complex, natural fen peat δ13C values were lower than those of the nearby bog, possibly due to the dominance of vascular plants on fen and the generally larger share of recycled C in the fens than in the bogs. Furthermore, natural and 51 years previously drained fen and bog, on the opposite sides of a ditch on the same mire complex, showed no significant differences in δ13C values. Plant δ13C values were lower, while δ13C values of subsoil were higher in the drained than in the natural site of the fen. 相似文献
8.
Tropical rainfall isotopic composition results from complex processes. The climatological and environmental variability in East Africa increases this complexity. Long rainfall isotope datasets are needed to fill the lack of observations in this region. At Kisiba Masoko, Tanzania, rainfall and rain isotopic composition have been monitored during 6 years. Mean year profiles allow to analyse the seasonal variations. The mean annual rainfall is 2099?mm with a rain-weighted mean composition of ?3.2?‰ for δ 18O and ?11.7?‰ for δ 2H. The results are consistent with available data although they present their own specificity. Thus, if the local meteoric water line is δ 2H?=?8.6 δ 18O?+?14.8, two seasonal lines are observed. The seasonality of the isotopic composition in rain and deuterium excess has been compared with precipitating air masses backtracking trajectories to characterize a simple scheme of vapour histories. The three major oceanic sources have two moisture signatures with their own trajectory histories: one originated from the tropical Indian Ocean at the beginning of the rainy season and one from the Austral Ocean at its end. The presented isotopic seasonality depends on the balance of the intertropical front and provides a useful dataset to improve the knowledge about local processes. 相似文献
9.
Po is the main Italian river and the δ 18O and δ 2H of its water reveal a similarity between the current meteoric fingerprint and that of the past represented by groundwater. As concerns the hydrochemisty, the Ca–HCO 3 facies remained constant over the last 50 year, and only nitrate significantly increased from less than 1?mg/L to more than 10?mg/L in the 1980s, and then attenuated to a value of 9?mg/L. Coherently, δ 13C DIC and δ 34S SO4 are compatible with the weathering of the lithologies outcropping in the basin, while extremely variable δ 15N NO3 indicates contribution from pollutants released by urban, agricultural and zootechnical activities. This suggests that although the origin of the main constituents of the Po river water is geogenic, anthropogenic contributions are locally significant. Noteworthy, the associated aquifers have the same nitrogen isotopic signature of the Po river, but are characterized by significantly higher NO – 3 concentration. This implies that aquifers’ pollution is not ascribed to inflow of current river water, and that the attenuation of the nitrogen load recorded in the river is not occurring in the aquifers, due to their longer water residence time and delayed recovery from anthropogenic contamination. 相似文献
10.
Arctic and sub-arctic watersheds are undergoing significant changes due to recent climate warming and degrading permafrost, engendering enhanced monitoring of arctic rivers. Smaller catchments provide understanding of discharge, solute flux and groundwater recharge at the process level that contributes to an understanding of how larger arctic watersheds are responding to climate change. The North Klondike River, located in west central Yukon, is a sub-alpine permafrost catchment, which maintains an active hydrological monitoring station with a record of >40 years. In addition to being able to monitor intra-annual variability, this data set allows for more complex analysis of streamflow records. Streamflow data, geochemistry and stable isotope data for 2014 show a groundwater-dominated system, predominantly recharged during periods of snowmelt. Radiocarbon is shown to be a valuable tracer of soil zone recharge processes and carbon sources. Winter groundwater baseflow contributes 20?% of total annual discharge, and accounts for up to 50?% of total river discharge during the spring and summer months. Although total stream discharge remains unchanged, mean annual groundwater baseflow has increased over the 40-year monitoring period. Wavelet analysis reveals a catchment that responds to El Niño and longer solar cycles, as well as climatic shifts such as the Pacific Decadal Oscillation. Dedicated to Professor Peter Fritz on the occasion of his 80th birthday 相似文献
11.
This paper presents the results of hydrological, physicochemical, biological, and isotopic investigations of the Danube River along the stretch through Serbian territory conducted during four campaigns in September and November 2007, September 2008 and April 2009. The stable isotope values exhibited significant changes both in the Danube (?10.7 to?9.5‰ for δ 18O and?73.7 to?67.1 ‰ for δ 2H) and in its tributaries (?9.1 to?8.5‰ for δ 18O and?69.4 to?59.4‰ for δ 2H) depending on the time of survey, which could be partly attributed to the influences of seasonal effects. Results emphasise the dominant role of tributaries inflows from aquifers along the Danube. The very narrow range of δ 13C POC (from?28.9 to?27.4 ‰) was associated with relatively high C/N ratios (C/N>9), and together with δ 15N TPN values, the date suggested that, in early spring, a major fraction of particulate organic matter was derived from allochthonous matter. An orthogonal varimax rotation of the principal components analysis identified four latent factors (‘mineral related’, ‘biological’, ‘hardness’, and ‘soil inlets’) which are responsible for the data structure covering 79% of the observed variations among the variables studied. A reliable grouping of samples with respect to the season was found. 相似文献
12.
We present a comparative study of two offline methods, a newly developed method and an existing one, for the measurement of the stable carbon isotopic composition (δ 13C) of dissolved inorganic carbon (DIC; δ 13C DIC) in natural waters. The measured δ 13C DIC values of different water samples, prepared from laboratory Na 2CO 3, ground and oceanic waters, and a laboratory carbonate isotope standard, are found to be accurate and reproducible to within 0.5 ‰\ (1σ). The extraction of CO 2 from water samples by these methods does not require pre-treatment or sample poisoning and can be applied to a variety of natural waters to address carbon cycling in the hydrosphere. In addition, we present a simple method (based on a two-end-member mixing model) to estimate the silicate-weathering contribution to DIC in a river system by using the concentration of DIC and its δ 13C. This approach is tested with data from the Krishna River system as a case study, thereby quantifying the contribution of silicate and carbonate weathering to DIC, particularly during peak discharge. 相似文献
13.
Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO 2 and water vapour were observed. The isotope ratios of both CO 2 and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ 13C–CO 2 and δ 18O–CO 2 increased, while δ 2H–H 2Ov and δ 18O–H 2Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO 2 and water vapour and the meteorological phenomena. Therefore, isotopic information of CO 2 and H 2Ov could be used as a tracer of meteorological information. 相似文献
14.
Data on modern radiocarbon activity in the old travertine formations of the Pymvashor hydrothermal system were used, in combination with 230Th/U dating of the travertine, to estimate the 14C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine ( 14C calc). With the known values of 14C calc and average age of the thermal water, and under the assumption that the residence time of the water in aquifer was constant over the last 13.9?±?1.5 ka, the initial 14C contents ( 14C 0) in the ancient thermal water were estimated. The findings in this study are that (1) both 14C 0 and δ 13С have decreased in young waters compared to the ancient waters; (2) although atmospheric 14C activity ( 14C atm) has also decreased in the same time, the decrease in 14C 0 is faster than the decrease in 14C atm. Under certain assumptions, one could link changes in 14C 0 and δ 13C to climate change. Decrease in δ 13С of soil CO 2 and decrease in 14C 0 was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in 14C atm. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO 2, caused by thawing permafrost. 相似文献
15.
Comparative biochemical and isotope-chemical investigations of cosmopolitical plants open up ways of obtaining parameters from different parts of the Earth which are characterised by variations in the habitat due to different environments. As an Antarctic oasis, the Schirmacher Oasis disposes of adequate favourable ecological conditions for the growth of lower plants. In the present paper, results of isotope studies of lichens, mosses and algae of the Schirmacher Oasis are given and peculiarities of the habitats which influence the isotope contents of the plants are discussed. 相似文献
16.
In the Basin and Range Province of the Southwestern U.S.A., deep carbonate groundwater has been suggested as a significant source to many overlying basin-fill alluvial aquifer systems. Notwithstanding, testing this hypothesis is limited by obtaining data from such considerable depths and complex geology. This study uses δ2H and δ18O data from springs, rivers, and wells tapping shallow basin-fill groundwater to test the hydrochemical interpretation of deep regional carbonate groundwater flow into the basin-fill aquifers. Stable isotopic and major ion attributes of hydrochemical facies suggest basin-fill alluvial groundwater of the Lower Virgin River Basin is a mixture of precipitation recharge within the Lower Virgin River Basin or the Clover and Escalante Desert Basin northwards, and the deep carbonate flow. The data support the conclusions that in the Lower Virgin River Basin, deep carbonate groundwater is an important source to the alluvial aquifer system and likely accounts for approximately 50% of the alluvial aquifer groundwater. Na+, K+, and SO42– increase in the basin-fill alluvial groundwaters outside the Virgin River floodplain appears to be related with upwelling of deep regional groundwater, and indicating that the chemical character of the basin-fill alluvial groundwaters are related to the deeper flow systems. 相似文献
17.
ABSTRACTChanges in groundwater evolutionary processes due to aquifer overexploitation show a world-wide increase and have been of growing concern in recent years. The study aimed to improve the knowledge of groundwater evolutionary processes by means of stable water isotopes and hydrochemistry in a representative lake basin, Ordos energy base. Groundwater, precipitation, and lake water collected during four campaigns were analysed by stable isotopes and chemical compositions. Results showed that temperature effect predominated the isotope fractionation in precipitation, while evaporation and inadequate groundwater recharge were the key factors explaining high salinity and isotopic enrichment in lake water. Additionally, the Kuisheng Lake was a preferential area of groundwater recharge, while the Subei Lake received less sources from underlying aquifer due to the combined effects of low permeable zone and upstream groundwater captured by the production wells. The homogeneous isotope signatures of groundwater may be ascribed to the closely vertical hydraulic connectivity between the unconfined and the confined aquifers. Isotopically enriched groundwater pumping from well field probably promoted isotopic depletion in groundwater depression cone. These findings not only provide the conceptual framework for the inland basin, but also have important implications for sustainable groundwater management in other groundwater discharge basins with arid climate. 相似文献
18.
Sulphate and chloride concentrations in the shallow Pleistocene aquifer systems in the lower Jordan valley area indicate a general trend of increasing salinity eastward and southward. This study was conducted in one of the important sub-basins feeding the Pleo–Pleistocene aquifer in the Jericho area in the southern part of the valley using S and O isotopes of dissolved sulphate. The results show that sulphate has mainly two contributions to the groundwater. One is the surface seepage, which is present as a salty leachate form with the positive δ 34S sulphate values of primary gypsum in Lisan and Samara formations, and the second is the upwelling saline water which was in contact with a deep secondary gypsum, aragonites and salty rocks and rose up under heavy abstraction with depleted 34S in sulphate and relatively high sulphate and chloride content. The latest was clearly shown in the Arab Project wells to the east that is undergoing a continuous heavy abstraction. The isotopic signatures of S and O in these wells to the east show that this depleted 34S and highly concentrated sulphate might also indicate a dissolved sulphate originating from pyrite oxidation that results from the interaction with a pyrite-rich aquifer, which can well up with salty water under heavy abstraction and is oxidised in the upper aerobic shallow aquifer. 相似文献
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